In lithography techniques, for example, a resist film composed of a resist material is formed on a substrate, and the resist film is subjected to selective exposure of radial rays such as light or electron beam through a mask having a predetermined pattern, followed by development, thereby forming a resist pattern having a predetermined shape on the resist film.
A resist material in which the exposed portions become soluble in a developing solution is called a positive-type, and a resist material in which the exposed portions become insoluble in a developing solution is called a negative-type.
In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have lead to rapid progress in the field of pattern miniaturization.
Typically, these miniaturization techniques involve shortening the wavelength (and increasing the energy) of the exposure light source. Conventionally, ultraviolet radiation typified by g-line and i-line radiation has been used, but nowadays KrF excimer lasers and ArF excimer lasers are starting to be introduced in the mass production of semiconductor elements. Furthermore, research is also being conducted into lithography techniques that use an exposure light source having a shorter wavelength (and a higher energy level) than these excimer lasers, such as electron beam, extreme ultraviolet radiation (EUV), and X-ray.
Resist materials for use with these types of exposure light sources require lithography properties such as a high resolution capable of reproducing patterns of minute dimensions, and a high level of sensitivity to these types of exposure light sources.
As a resist material that satisfies these conditions, a chemically amplified resist composition is used, which includes a base component which exhibits changed solubility in an alkali developing solution under the action of acid and an acid generator that generates acid upon exposure.
For example, a positive-type chemically amplified resist composition typically contains a resin component (base resin) which exhibits increased solubility in an alkali developing solution under the action of acid, and an acid generator component. If the resist film formed using this resist composition is selectively exposed during formation of a resist pattern, then within the exposed portions, acid is generated from the acid generator, and the action of this acid causes an increase in the solubility of the resin component in an alkali developing solution, making the exposed portions soluble in the alkali developing solution.
Currently, resins that contain structural units derived from (meth)acrylate esters within the main chain (acrylic resins) are widely used as base resins for resist compositions that use ArF excimer laser lithography or the like, as they exhibit excellent transparency in the vicinity of 193 nm (for example, see Patent Document 1).
As acid generators usable in chemically amplified resist compositions, various types have been proposed including, for example, onium salt acid generators such as iodonium salts and sulfonium salts, oxime sulfonate acid generators, diazomethane acid generators, nitrobenzylsulfonate acid generators, iminosulfonate acid generators, and disulfone acid generators.
Among these, onium salt acid generators having an onium ion such as triphenylsulfonium as the cation moiety are widely used as acid generators. The anion moiety of these onium salt acid generators is typically an alkylsulfonate ion or a fluorinated alkylsulfonate ion in which some or all of the hydrogen atoms of the alkyl group have been substituted with fluorine atoms.
Further, resist compositions containing a fluorine-containing sulfonate onium salt represented by formula (1) shown below or an onium salt having an anion represented by formula (2) shown below as the acid generator have also been disclosed (see Patent Documents 2 and 3).
In formula (1), R1 represents a monovalent organic group, and Q+ represents a sulfonium cation or an iodonium cation. In formula (2), n represents an integer of 1 to 3.